Copyright gives the creator of a protected work the exclusive right to authorize copying the work or creating a "derivative work". It does not give the copyright owner the exclusive right to "use" the work. As software, fonts (not typefaces) are protected.
In order to create a book, you "use" a font on your computer, which (presumably) legally installed e.g. as part of the operating system, which you have a license to "use". Your publishing software extracts information about the font and characters used, and refers to those properties but usually does not copy the font into the document. Others who have the same or similar font then read the document, and their operating system uses that information to access (licensed) fonts on their computer.
We don't need to get into technical details of how fonts work, what matters for our purposes is that no copying of the font is done, except when a font is installed. If a person gets a font from a pirate source, that would be copyright infringement, but the infringement lies in the downloading / installing, not the using. It is possible that a particular font has special usage restrictions in the license. If the font comes with your operating system, it is most likely that the copy is legal, but if you download it from some website, then you would need to do research to determine if they have the right to distribute the font, and whether the license imposes any restrictions on your use.
